The laser disc of the present invention is the central part of laser disc mass memories, set forth by U.S. Pat. Nos. 3,314,073; 3,474,457; 3,654,624; 3,665,483; and 4,001,840 by Becker, and Becker et al. These patents disclose digital disc storage and retrieval of extreme bandwidths (&gt;50 Mbit/s), linear densities (2.sup.8 =256), and storage capacities (10.sup.10 bit/disc), by means of creating diffraction-limited "holes" (bits) within laser-focus in thin metal films. The diameter (d) of these holes (bits) is determined by the Rayleigh-Sommerfield condition of diffraction: EQU d=122.lambda.f/D
wherein 1.22 is the first root of a Bessel function, ".lambda." is the laser wavelength, "f" is the focal length of the laser focusing objective and "D" is its effective circular aperture diameter (U.S. Pat. No. 3,314,073 by Becker).
The bandwidth of a laser disc storage and retrieval system is determined by the thermodynamics of laser-storage, yielding the characteristic dependence of the bit-creating laser power from the square root of the laser recording frequency (U.S. Pat. No. 3,474,457 by Becker). Minimum laser power is obtained by means of utilizing low-melting thin metal films, like Indium, Tin, etc.
In order to protect the thin metal film against physical damage, dust depositions and deterioration, the film is covered with a transparent layer of a dielectric material (U.S. Pat. No. 3,654,624 by Becker et al). The electronics and kinematics of laser mass storage and retrieval are determined by phase-lock and servo-controls with a mirror galvanometer (U.S. Pat. No. 3,665,483 by Becker et al).
Non-photographic digital laser image recording and reading provides visual, two-dimensional replicas or representations of objects, pictures, illustrations, video-pictures, computer outputs, and the like. It utilizes flat-field optical laser-scanning with laser-beams, focused to a diffraction-limited spot on a radiation sensitive material, e.g., a heat ablatable or vaporizable recording medium, to create in read-time a two-dimensional ensemble of "holes" in the laser-recording medium. The visual laser record is an instantaneous replica of an original image or its computer processed binary equivalent (U.S. Pat. No. 4,001,840 by Becker et al).
In Becker et al U.S. Pat. No. 4,001,840 disclosure is made of a vacuum encapsulation with a space surrounding the metal thin film. In Day et al U.S. Pat. No. 4,038,663 a stream of filtered gas is passed through the space between a covering foil and the writing surface. These structures cannot have an optically perfect interface between the protective coating and the writing surface.
The laser technology thus described will be particularly utilized for the permanent laser storage and retrieval of wideband, digital data, transmitted from satellites. These techniques will be used for satellite exploration of the earth in opto-electronic processes which are designated as "laser remote sensing". The principles of laser remote sensing may be summarized as follows.
After the read-time primary laser disc storage of the raw, digital satellite signals, and after subsequent electronic correction of these data with a large computer, the flexible laser disc stores the computer-output for the "users" and their "remote sensing" operation. They obtain laser-copies of the laser discs by air-mail, as well as photographic copies of the corresponding real images. These are produced in separate, photographic laser recording processes, thus yielding optimum correlation between the digital image data and their equivalent analogous color images.
With the enormous quantities of laser discs required in the future for laser remote sensing with earth satellites, considering 10.sup.10 bit/disc and 10.sup.12 bit/day of satellite data to be stored per ground station, as well as the global distribution of the data for the "users" expected to encompass 400 remote sensing stations all over the world, the laser disc should be utmost reliable, interchangeable, permanent, and of practically unlimited archival life. Laser disc storage should be indefinitely protected against deposition of dust particles, physical damages and deterioration. Based on these considerations, it is the main purpose of this invention to provide means to produce laser discs which comply with the preceding requirements.
In accordance with the present invention a flexible disc for laser disc mass storage and retrieval of data is provided, along with a method of manufacturing the same, wherein a vacuum deposited metal thin-film of low melting point metal is vacuum encapsulated within saturated polyester plastic during processing in a vacuum chamber. There is no space between the metal thin film and the plastic. There is an optically perfect interface between the metal thin film and the plastic.
In one embodiment the metal film is vacuum deposited on a disc layer of saturated polyester plastic, and the metal film is covered with a layer of saturated polyester plastic.
In another embodiment the metal film is coated on the opposed broad surfaces of a glass plate and then a layer of saturated polyester plastic is coated over the metal film on each of the glass plate surfaces.